Working Rat Heart Research Articles

Using an Isolated Working Rat Heart Model to Test Donor Heart Preservation Strategies.

Optimization of donor heart preservation solutions has played a key role in reducing ischemia-reperfusion injury in donor hearts during organ retrieval, transportation, and transplantation. Previous work from our laboratory showed that the addition of glyceryl trinitrate and erythropoietin to donor heart preservation solutions could significantly improve cardiac functional recovery after prolonged cold storage and in donation after circulatory death hearts. This supplementation protocol has been implemented in clinical use in transplant units around Australia, Belgium, and the United Kingdom. Here, we outline a protocol for testing supplementation strategies using an ex vivo isolated working rat heart (IWRH) perfusion circuit. Using this methodology, supplementation strategies can be tested in the context of prolonged cold static storage, donation after brain death, and donation after circulatory death donor heart preservation. Cardiac functional recovery, measured by aortic flow, coronary flow, cardiac output, pulse pressure, and heart rate, can be used to determine whether a particular preservation strategy can minimize ischemia-reperfusion injury of the donor heart.

Abstract P2184: Isocitrate Dehydrogenase 1 Regulates Cardiac Metabolic Adaptation During Oncometabolic Stress

Cardiovascular disease and cancer are the two leading causes of morbidity and mortality in the world. Metabolic dysregulation of cancer cells extends beyond the tumor microenvironment and increases risk for cardiovascular diseases. One common somatic mutation in cancer cells affects isocitrate dehydrogenase (IDH) 1 and 2, which catalyzes the oxidative decarboxylation of isocitrate to alpha-ketoglutarate in the cytosol and mitochondria, respectively. IDH1 and 2 mutations cause the production of the oncometabolite D-2-hydroxyglutarate (D2-HG) which allosterically inhibits alpha-ketoglutarate dehydrogenase (alpha-KGDH) and is associated with reduced cardiac contractile function. We combined stable isotope tracer studies with computational modeling to study the fundamental role of IDH isoforms for cardiac adaptation during oncometabolic stress. We uncovered an unexpected cardiac phenotype that expands the role of IDH1 in the heart beyond oxidative metabolism. Using mass spectrometry-based metabolomics, we quantified the stable isotopomer distributions from glucose and glutamine in perfused working rat hearts and isolated adult ventricular cardiomyocytes. Our analysis revealed that defective mitochondrial metabolism causes redirection of carbon flux oxidative towards reductive pathways. Reductive carboxylation of alpha-KGDH increases glutamine uptake and glutamine-derived citrate formation in both working rat heart perfusions and cultured adult mouse ventricular cardiomyocytes. To identify which IDH isoform is responsible for redirecting carbon flux, we developed knockout models of IDH1, 2, and 3 in adult mouse ventricular cardiomyocytes. Loss of IDH1 expression impaired reductive formation of citrate and caused functional defects in cardiomyocytes. Lastly, epigenetic analyses of histone marks revealed that IDH1 causes widespread alterations in histone acetylation and tri-methylation. Our results highlight a novel role for IDH1 in cardiac metabolism and transcriptional control of metabolic adaptation in response to tumor-mediated stress and provide evidence of how reductive-citrate formation may induce epigenetic modifications in the heart.

Assessment of Cardiac Toxicity of Manganese Chloride for Cardiovascular Magnetic Resonance

MRI is widely used in cardiology to characterize the structure and function of the heart. Currently, gadolinium-based contrast agents are widely used to improve sensitivity and specificity of diagnostic images. Recently, Manganese, a calcium analogue, has emerged as a complementary contrast agent with the potential to reveal remaining viable cells within altered tissue. Imaging applications may be limited by substantial toxicity of manganese. Indeed, cardiac safety of manganese is not yet comprehensively assessed. In this study we investigated the effect of MnCl2 (1–100 µM) on cardiac function. Hemodynamic function was determined ex vivo using an isolated working rat heart preparation. HL-1 cardiac myocytes were used to investigate cell viability (calcein AM) and calcium cycling (Cal-520 a.m.). Rat ventricular cardiomyocytes were dissociated by enzymatic digestion. Action potentials and calcium currents were recorded using the patch clamp technique. MRI experiments were performed at 1.5T on formalin-fixed rat hearts, previously perfused with MnCl2. MnCl2 perfusion from 1 up to 100 µM in isolated working hearts did not alter left ventricular hemodynamic parameters. Contractility and relaxation index were not altered up to 50 µM MnCl2. In HL-1 cardiac myocytes, incubation with increasing concentrations of MnCl2 did not impact cell viability. The amplitude of the calcium transients were significantly reduced at 50 and 100 µM MnCl2. In freshly isolated ventricular myocytes, action potential duration at 20, 50 and 90% of repolarization were not modified up to 10 µM of MnCl2. L-type calcium current amplitude was significantly decreased by 50 and 100 µM of MnCl2. MRI on heart perfused with 25 and 100 µM of MnCl2 showed a dose dependent decrease in the T1 relaxation time. In conclusion, our results show that low concentrations of MnCl2 (up to 25 µM) can be used as a contrast agent in MRI, without significant impact on cardiac hemodynamic or electrophysiology parameters.

Assessment of cardiac toxicity of manganese chloride for cardiovascular magnetic resonance

MRI is widely used in cardiology to visualize the structure and function of the heart. Currently gadolinium is the contrast agents use to improve sensitivity and specificity of diagnostic images, enabling the assessment of scar and fibrosis. Manganese-based contrast molecules are being developed with the hope to improve the diagnosis of cardiac pathologies. Manganese, a calcium analogue, allows detection of viable cells within altered tissue. However, the cardiac safety of manganese is not fully assessed. To characterize the effect of MnCl2 on cardiac function and electrical parameters. Hemodynamic function was determined ex vivo using the isolated working rat heart preparation. HL-1 cell line was used to investigate cell viability (loading with calcein AM) and calcium cycling (loading with CAL-520 AM). Rat ventricular cardiomyocytes were dissociated by enzymatic digestion. Action potentials and calcium currents were recorded using the patch clamp technique. The effect of ascending concentrations of MnCl2 (1, 10, 25, 50 and 100 μM) were evaluated. MRI experiments (1.5 T and 9.4 T) were performed on formalin-fixed rat hearts, previously perfused with 25 or 100 μM of MnCl2. Left ventricular hemodynamic parameters from isolated working hearts show that heart rate is not modified by μM [MnCl2]. Similar observation was made for contractility index and aortic flow up to 50 μM; 100 μM MnCl2 induced a significant decrease of the two parameters. At the cellular level, μM [MnCl2] did not impact HL-1 cell viability. The amplitude of the calcium transients was significantly reduced only at 100 μM of MnCl2 ( P < 0.05). In isolated ventricular myocytes, action potential duration at 20%, 50% and 90% of repolarization were not modified up to 10 μM of MnCl2. A small but significant decrease of action potential duration was observed at 25, 50 and 100 μM (APD90 decrease by 23 ± 6% vs control). Peak L-type calcium current amplitude was significantly decreased by 50 and 100 μM of MnCl2. MRI on heart perfused with 25 μM of MnCl2 (no impact hemodynamic function) and 100 μM of MnCl2 showed a dose dependent decrease in the T1 relaxation time, a parameter for altered and disease state. Our results show that μM [MnCl2] (up to 25 μM) can be used as a contrast agent in MRI, without effects on cardiac hemodynamic parameters. MRI with manganese should therefore enable visualization of viable and stunned myocardium.

A Foot Soldier in Cardiac Metabolism: A Conversation With Heinrich Taegtmeyer, MD, DPhil.

A Foot Soldier in Cardiac Metabolism: A Conversation With Heinrich Taegtmeyer, MD, DPhil.

Abstract 10973: Tenascin-C Deficiency Rescues the Effect of Diabetes on Cardiac and Vascular Dysfunction in Mice

Introduction: Tenascin-C (TN-C) upregulation is linked to worse clinical outcome in diabetic patients. However, the role of TN-C in the development of diabetic cardiomyopathy is still unknown. Hypothesis: Whether TN-C plays a maladaptive role in diabetic cardiomyopathy. Methods: AJ (n=14) and TNC-KO (n=16) adult male mice were injected with streptozotocin (50mg/kg) to induce diabetes. Cardiac function was measured by echocardiography at 16-18 weeks follow-up. Additionally, cardiomyocyte passive stiffness , vascular endothelial function (aorta), and cardiac fibrosis were assessed. In addition, the hemodynamic effect of human recombinant TN-C (hrTN-C; 80 ng/ml) on the isolated working rat heart (n=3) was evaluated. Isolated primary mouse cardiomyocytes (IPMC) were used to assess TN-C expression. Human ventricular cardiac fibroblasts (HCF) were cultured and treated with 1) TGF-β (20ng/ml); 2) rhTN-C (10μg/ml) and TLR4 inhibitor (TAK-242, 50 mM) in combination with TN-C and mRNA expression of α-SMA, TN-C, Col-1, Col-3 and ACE1 were assessed by RT-qPCR. Finally, HUVEC were treated either with rhTN-C (10μg/ml) or combination with TLR-4 inhibitor and analysed of the expression of NADPH oxidase 1 and 4 (NOX1, NOX4). Results: TN-C deficiency was accompanied by preserved LV ejection fraction and endothelium function in aorta (p&lt;0.05, respectively). Diabetic TN-C KO mice show reduction in cardiomyocyte stiffness and diastolic dysfunction as compared to AJ diabetic group (p&lt;0.01). Histology revealed less cardiac and perivascular fibrosis in diabetic TN-C KO animals than in the AJ diabetic group (p&lt;0.01). In addition, rhTN-C resulted in reduction in cardiac function in isolated rat hearts. mRNA expression of TN-C was increased in IPMC. Moreover, TGF-β treatment markedly upregulated TN-C expression (p&lt;0.01) and rhTN-C promoted pro-fibrotic genes expression (p&lt;0.05, respectively). HUVEC incubated with rhTN-C showed increased expression of IL-6 and NOX4 via TLR-4 signalling. Conclusions: TN-C promotes a hostile environment that facilitates fibrosis and oxidative stress leading to cardiomyocyte and endothelial cell dysfunction. Thus, TN-C may play a crucial role in cardiovascular dysfunction in diabetes as well as a potential target for therapy.

Pre-ischemic Lactate Levels Affect Post-ischemic Recovery in an Isolated Rat Heart Model of Donation After Circulatory Death (DCD).

Introduction: Donation after circulatory death (DCD) could substantially improve donor heart availability. In DCD, the heart is not only exposed to a period of warm ischemia, but also to a damaging pre-ischemic phase. We hypothesized that the DCD-relevant pre-ischemic lactate levels negatively affect the post-ischemic functional and mitochondrial recovery in an isolated rat heart model of DCD.Methods: Isolated, working rat hearts underwent 28.5′ of global ischemia and 60′ of reperfusion. Prior to ischemia, hearts were perfused with one of three pre-ischemic lactate levels: no lactate (0 Lac), physiologic lactate (0.5 mM; 0.5 Lac), or DCD-relevant lactate (1 mM; 1 Lac). In a fourth group, an inhibitor of the mitochondrial calcium uniporter was added in reperfusion to 1 Lac hearts (1 Lac + Ru360).Results: During reperfusion, left ventricular work (heart rate-developed pressure product) was significantly greater in 0.5 Lac hearts compared to 0 Lac or 1 Lac. In 1 vs. 0.5 Lac hearts, in parallel with a decreased function, cellular and mitochondrial damage was greater, tissue calcium content tended to increase, while oxidative stress damage tended to decrease. The addition of Ru360 to 1 Lac hearts partially abrogated the negative effects of the DCD-relevant pre-ischemic lactate levels (greater post-ischemic left ventricular work and less cytochrome c release in 1 Lac+Ru360 vs. 1 Lac).Conclusion: DCD-relevant levels of pre-ischemic lactate (1 mM) reduce contractile, cellular, and mitochondrial recovery during reperfusion compared to physiologic lactate levels. Inhibition of mitochondrial calcium uptake during early reperfusion improves the post-ischemic recovery of 1 Lac hearts, indicating calcium overload as a potential therapeutic reperfusion target for DCD hearts.

Pre-Ischemic Lactate Levels Affect Post-Ischemic Functional Recovery in an Isolated Rat Heart Model of Donation after Circulatory Death (DCD)

Purpose Donation after circulatory death (DCD) could substantially improve donor heart availability. In DCD, the heart is not only exposed to a period of warm ischemia, but also to a damaging pre-ischemic phase after withdrawal of life support. We investigated the effects of different pre-ischemic lactate levels on post-ischemic recovery using an isolated rat heart model of DCD. Methods Isolated, working rat hearts underwent 20’ aerobic perfusion, 28.5’ global ischemia, and 60’ reperfusion. In addition to 11 mM glucose and 1.2 mM palmitate, three pre-ischemic lactate levels were tested: no lactate (0 Lac), physiologic lactate (0.5 mM; 0.5 Lac), or DCD-relevant lactate (1 mM; 1 Lac). Contractile function, mitochondrial integrity and potential mediators of injury were evaluated. Results During reperfusion, left ventricular work (heart rate-developed pressure product) was significantly greater in 0.5 Lac hearts compared to 0 Lac or 1 Lac. In 0.5 Lac vs 0 Lac hearts, in parallel with increased function, cytochrome c release and carbonylated protein levels were significantly reduced, indicating less mitochondrial damage and oxidative stress, respectively. In 1 Lac vs 0.5 Lac hearts, in parallel with decreased function, cytochrome c release tended to increase, but carbonylated protein levels tended to decrease. Conclusion DCD-relevant levels of pre-ischemic lactate (1 mM) reduce contractile recovery during reperfusion compared to physiologic levels. Although increased pre-ischemic lactate tends to lower oxidative stress during reperfusion; this, alone, is insufficient to maintain functional recovery at DCD-relevant levels. Further investigations are ongoing to clarify underlying mechanisms.

Mitochondrial oxidative phosphorylation and mitophagy in myocardial ischaemia/reperfusion: effects of chloroquine.

The aim of this study was to evaluate the temporal relationship between mitochondrial oxidative phosphorylation and mitophagy in rat hearts subjected to ischaemia/reperfusion. Measurements were made at specific points during the experimental protocol (snapshot approach) and by assessments of mitophagic flux, using chloroquine pre-treatment. Isolated working rat hearts were subjected to 25 or 30 minutes of global ischaemia/10 minutes of reperfusion. Half of each group received chloroquine (10 mg/kg, intraperitoneally) one hour before experimentation. Mitochondria were isolated after stabilisation, ischaemia and reperfusion, and oxidative phosphorylation was measured polarographically. Mitochondrial mitophagy markers were detected by Western blot analysis. Mitochondrial oxygen uptake (state 3) and oxidative phosphorylation rate were reduced by ischaemia and increased by reperfusion. Chloroquine pre-treatment increased both parameters. Using a snapshot approach, exposure to ischaemia ± reperfusion had little effect on mitochondrial PINK1, Parkin and p62/SQSTM1 expression. Ischaemia reduced Rab9 expression, and reperfusion upregulated the phosphor DRP1, phosphor/total DRP1 ratio and Rab9 levels. Chloroquine significantly reduced PINK1, p62/SQSTM1, Rab9 and particularly Parkin expression during reperfusion, without an effect on mitochondrial total and phospho DRP1 levels. Ischaemia/reperfusion-induced changes in mitochondrial oxidative phosphorylation function occurred concomitantly with changes in mitophagic flux. Pre-treatment with chloroquine profoundly affected mitochondrial function as well as the pattern of mitophagy during ischaemia/reperfusion.

Abstract 308: Reductive Carboxylation Contributes to Cardiac Adaptation in Response to the Oncometabolite D2-hydroxyglutarate

Cancer cells rewire metabolism to support tumor growth and proliferation. In isocitrate dehydrogenase (IDH) 1 and 2 mutant tumors, increased plasma levels of the oncometabolite D-2-hydroxyglutarate (D2-HG) are associated with systemic effects, including myopathy. D2-HG causes inhibition of alpha-ketoglutarate dehydrogenase (AKGDH), which is associated with reduced cardiac contractile function. How tumor cells influence the metabolism of cardiomyocytes remains mostly unknown. Specific cancer cells use glutamine-dependent reductive carboxylation to circumvent defective mitochondrial metabolism by producing citrate and acetyl-CoA for lipid synthesis, which tumors require for growth. Here, we explore the hypothesis that inhibition of AKGDH by the oncometabolite D2-HG increases glutamine-dependent reductive carboxylation in the heart. We combined ex vivo rat heart perfusions with mass-spectrometry-based stable isotope tracer studies and in silico metabolic flux analysis. In response to D2-HG-mediated inhibition of AKGDH, we observed an increased reductive carboxylation of alpha-ketoglutarate to citrate rather than oxidative decarboxylation. This pathway increases glutamine uptake and glutamine-derived citrate formation in both working rat heart perfusions and cultured adult mouse ventricular cardiomyocytes. When we perfused rat hearts with 13C-labelled D2-HG, we observed a similarly increased formation of citrate. To identify which IDH isoform is responsible for redirecting carbon flux, we modulated IDH1, 2, and 3 in adult mouse ventricular cardiomyocytes using siRNAs. Reduced expression of IDH1 impaired reductive formation of citrate. Importantly, we observed a significant correlation between reductive citrate formation and epigenetic modifications of histones, including increased histone 3 lysine 9 acetylation and di-methylation. To explore these observations, we conducted ChIP-sequencing and identified distinct transcriptional remodeling. Taken together, we demonstrate how oncometabolic stress in the heart causes redirection of central carbon metabolism via reductive carboxylation, and provide evidence of how reductive-citrate formation may induce epigenetic modifications in the heart.

P561Acute effects of dronedarone and amiodarone on functional, morphological and oxidative stress parameters in isolated rat heart with hypertension

Abstract Introduction Amiodarone represents the most widely used antiarrhythmic drug, even though it has been shown that it has negative inotropic and lusitropic effect in healthy hears. On the other hand, dronedarone reduces the risk of recurrent atrial fibrillation, but with increased early mortality related to the worsening of heart failure. However, the mechanisms responsible for these fatal outcomes remain unclear and require further examinations. Purpose To investigate acute, direct effects of Dronedarone and Amiodarone on cardiac contractility, coronary flow and oxidative stress parameters in isolated rat heart with hypertension. Methods The present study was carried out on 18 isolated hearts of spontaneously hypertensive Wistar Kyoto male rats (6 weeks old, bodyweight 200 ± 10 g). After isolation, all hearts were retrogradely perfused according to Langendorff technique with a gradually increment of coronary perfusion pressure (CPP from 40 to 120 cm H2O) and randomly divided into 3 groups: Control (n = 6), Amiodarone (n = 6, isolated hearts perfused with Amiodarone in dose of 3 umol), Dronedarone (n = 6, isolated hearts perfused with Dronedarone in dose of 1.8 umol). During ex vivo protocol continuously were registered cardiac contractility parameters and coronary flow, while from collected coronary venous effluent markers of oxidative stress were measured. All hearts were then fixated and stained with Hematoxylin/eosin. Results Dronedarone severely depressed the function of all cardiodynamic parameters of the heart compared with Amiodarone or Control while Amiodarone intensified the function of the isolated rat heart with hypertension compared to Control (dp/dt max mmHg/s at coronary perfusion pressure 120cmH2O Dronedarone vs. Amiodarone vs. Control 579.733 ± 202.27 vs. 3063.65 ± 467.93 vs. 2682.88 ± 368.75; p &amp;lt; 0.001. dp/dt min mmHg/s 120cmH2O -352.13 ± 204.65 vs. 1960 ± 242.21 vs. -1858.83 ± 118.23; p &amp;lt; 0.001. SLVP mmHg at CPP 120cmH20 27.8 ± 3.46 vs. 98.95 ± 11.78 vs. 71.45 ± 7.56; p &amp;lt; 0.001. DLVP mmHg at CPP 120cmH2O 6.32 ± 0.49 vs. 4.83 ± 0.54 vs. 0.85 ± 0.35; p &amp;lt; 0.001). Acute administration of Dronedarone decreased the level of NO2- and increased the level of H2O2 , while Amiodarone heightens O2- levels (O2- nmol/min g wt at coronary perfusion pressure 120cmH2O Dronedarone vs. Amiodarone vs. Control 28.62 ± 2.54 vs. 77.3 ± 8.86 vs. 31.72 ± 4.56; p &amp;lt; 0.001. H2O2 nmol/min g wt at CPP 120cmH2O 92.56 ± 11.65 vs. 48.63 ± 10.11 vs. 42.84 ± 84; p &amp;lt; 0.001. NO2- nmol/min g wt at CPP 120cmH2O 38.61 ± 4.94 vs. 82.28 ± 5.76 vs. 64.71 ± 3.51; p &amp;lt; 0.001). Pathohistological, structural changes were observed in both, experimental groups. Conclusions Acute administration of Dronedarone depresses cardiac function in isolated, working rat heart with hypertension, with decreasing the NO2- levels, increasing the level of H2O2 and enhanced structural changes when compared to Amiodarone.

Cytosolic, but not matrix, calcium is essential for adjustment of mitochondrial pyruvate supply

Mitochondrial oxidative phosphorylation (OXPHOS) and cellular workload are tightly balanced by the key cellular regulator, calcium (Ca2+). Current models assume that cytosolic Ca2+ regulates workload and that mitochondrial Ca2+ uptake precedes activation of matrix dehydrogenases, thereby matching OXPHOS substrate supply to ATP demand. Surprisingly, knockout (KO) of the mitochondrial Ca2+ uniporter (MCU) in mice results in only minimal phenotypic changes and does not alter OXPHOS. This implies that adaptive activation of mitochondrial dehydrogenases by intramitochondrial Ca2+ cannot be the exclusive mechanism for OXPHOS control. We hypothesized that cytosolic Ca2+, but not mitochondrial matrix Ca2+, may adapt OXPHOS to workload by adjusting the rate of pyruvate supply from the cytosol to the mitochondria. Here, we studied the role of malate-aspartate shuttle (MAS)-dependent substrate supply in OXPHOS responses to changing Ca2+ concentrations in isolated brain and heart mitochondria, synaptosomes, fibroblasts, and thymocytes from WT and MCU KO mice and the isolated working rat heart. Our results indicate that extramitochondrial Ca2+ controls up to 85% of maximal pyruvate-driven OXPHOS rates, mediated by the activity of the complete MAS, and that intramitochondrial Ca2+ accounts for the remaining 15%. Of note, the complete MAS, as applied here, included besides its classical NADH oxidation reaction the generation of cytosolic pyruvate. Part of this largely neglected mechanism has previously been described as the “mitochondrial gas pedal.” Its implementation into OXPHOS control models integrates seemingly contradictory results and warrants a critical reappraisal of metabolic control mechanisms in health and disease.

Empagliflozin Improves Cardiac Functional Recovery after Prolonged Cold Storage of Donor Hearts in an Isolated Working Rat Heart Model

Many donor hearts are unsuitable for transplantation after prolonged cold storage or donation after circulatory death. Improved donor heart recovery is observed after supplementation of preservation solutions with sodium-hydrogen exchange inhibitors (NHEI) cariporide/zoniporide (Gao et al, 2010, BJP; Cropper et al, 2003, JHLT). NHEI are not clinically used due to neurotoxicity observed in cariporide clinical trials however the search for suitable NHEI alternatives continues. One promising alternative is the sodium-glucose cotransporter 2 inhibitor Empagliflozin (Empa) - the first anti-diabetic drug to yield positive cardiovascular outcomes. Studies have shown Empa mimics NHEI and slows pH recovery in cardiomyocytes following an acidic load. This study tests the cardioprotective efficacy of Empa-supplementation in cardiac preservation solution during prolonged cold storage of donor hearts. Wistar rat (320-420g; n=5-7) hearts were perfused ex-vivo and baseline hemodynamic measurements acquired. Hearts were arrested and stored in Celsior±0.3-10µM Empa, or zoniporide (1µM) (6h, 4°C) then reperfused (37°C, Langendorff 15min, working 30min). Post-reperfusion aortic flow (AF) and cardiac output (CO) were expressed as a percentage of baseline measurements. Coronary effluent (pre-storage, 15, 30, and 45 min reperfusion) was assessed for lactate dehydrogenase (LDH) release. Donor hearts supplemented with Empa during cold storage showed a dose-dependent improvement in cardiac functional recovery. Compared to unsupplemented control hearts, 10µM Empa-supplemented hearts showed significantly improved AF (54±11% vs 10±7%, p=0.006) and CO (55±12 vs 16±8, p=0.03) recovery. Hearts supplemented with 1µM zoniporide also showed significantly improved AF (63±7%, p=0.002 vs control) and CO (65±9%, p=0.01) recovery. A trend for reduced LDH efflux was observed in hearts supplemented with 1-10µM Empa or zoniporide compared to control hearts. Supplementation of cardiac preservation solution with 10µM Empa yields significantly improved functional recovery after prolonged cold storage, with similar cardioprotective efficacy to the NHEI zoniporide. Given the approved clinical use of Empa, this study highlights its potential as a suitable alternative for NHEI in donor heart preservation.

Cyclosporine A as a Cardioprotective Agent During Donor Heart Retrieval, Storage, or Transportation: Benefits and Limitations

Storage of donor hearts in cardioplegic solutions supplemented with conditioning agents activating endogenous mitochondrial protective signaling enhanced their postreperfusion recovery. The present study investigates the role of timing and duration of cardiac exposure to cyclosporine A (CsA), another putative mitochondrial protectant, on cardiac functional recovery and potential mechanisms of CsA action in an isolated working rat heart model of donor heart retrieval and storage. After measurement of baseline function, hearts were arrested and stored for 6 hours at 4°C in either Celsior alone or Celsior + CsA (0.2 µM), then reperfused for 45 minutes in Krebs solution, when functional recovery was assessed. Two additional groups of Celsior-alone stored hearts were exposed to 0.2 µM CsA for the initial 15 minutes (nonworking period) or the full 45-minute period of reperfusion. Coronary effluent was collected pre- and poststorage for assessment of lactate dehydrogenase release. Tissue samples were collected at the end of each study for immunoblotting and histological studies. CsA supplementation during cold storage or the first 15-minute reperfusion significantly improved functional recovery and significantly increased phospho-AMPKαThr172 and phospho-ULK-1Ser757. Hearts exposed to CsA for 45 minutes at reperfusion recovered poorly with no phospho-AMP-activated protein kinase α activation, decreased phospho-eNOSSer633, and decreased mitochondrial cytochrome c content with increased lactate dehydrogenase release. Inclusion of CsA during cold storage is cardioprotective. Effects of CsA addition to the perfusate during reperfusion were time dependent, with benefits at 15 minutes but not 45 minutes of reperfusion. The toxic effect with the presence of CsA for the full 45-minute reperfusion is associated with impaired mitochondrial integrity and decreased eNOS phosphorylation.

Heinrich Taegtmeyer: "All is in Flux".

Heinrich Taegtmeyer: "All is in Flux".

Electrically-Induced Ventricular Fibrillation Alters Cardiovascular Function and Expression of Apoptotic and Autophagic Proteins in Rat Hearts.

Background: The pathological heart contractions, called arrhythmias, especially ventricular fibrillation (VF), are a prominent feature of many cardiovascular diseases leading to sudden cardiac death. The present investigation evaluates the effect of electrically stimulated VF on cardiac functions related to autophagy and apoptotic mechanisms in isolated working rat hearts. Methods: Each group of hearts was subjected to 0 (Control), 1, 3, or 10 min of spacing-induced VF, followed by 120 min of recovery period and evaluated for cardiac functions, including aortic flow (AF), coronary flow (CF), cardiac output (CO), stroke volume (SV), and heart rate (HR). Hearts were also evaluated for VF effects on infarcted zone magnitude and Western blot analysis was conducted on heart tissue for expression of the apoptotic biomarker cleaved-caspase-3 and the autophagy proteins: p62, P-mTOR/mTOR, LC3BII/LC3BI ratio, and Atg5-12 complexes. Results: Data revealed that VF induced degradation in AF, CF, CO, and SV, which prominently included-variable post-VF capacity for recovery of normal heart rhythm; increased extent of infarcted heart tissue; altered expression of cleaved-caspase-3 suggesting potential for VF-mediated amplification of apoptosis. VF influence on expression of p62, LC3BII/LC3BI, and Atg5-12 proteins was complex, possibly due to differential effects of VF-induced expression on proteins comprising the autophagic program. Conclusions: VF was observed to cause time-dependent changes in autophagy processes, which with additional analysis under ongoing investigations, likely to yield novel therapeutic targets for the prevention of VF and sudden cardiac death.

The impact of sugar-sweetened beverage intake on rat cardiac function

AimsAlthough there is evidence linking sugar-sweetened beverage (SSB) intake with the development of cardio-metabolic diseases, the underlying mechanisms remain unclear. The current study therefore evaluated the effects of SSB consumption by establishing a unique in-house in vivo experimental model. Main methodsMale Wistar rats were divided into two groups: a) one consuming a popular local SSB (SSB- Jive), and b) a control group (Control-water) for a period of three and six months (n = 6 per group), respectively. Rats were gavaged on a daily basis with an experimental dosage amounting to half a glass per day (in human terms) (SSB vs. water). Cardiac function was assessed at baseline (echocardiography) and following ex vivo ischemia-reperfusion of the isolated perfused working rat heart. Oral glucose tolerance tests and mitochondrial respiratory analyses were also performed. In addition, the role of non-oxidative glucose pathways (NOGPs), i.e. the polyol pathway, hexosamine biosynthetic pathway (HBP) and PKC were assessed. Key findingsThese data show that SSB intake: a) resulted in increased weight gain, but did not elicit major effects in terms of insulin resistance and cardiac function after three and six months, respectively; b) triggered myocardial NOGP activation after three months with a reversion after six months; and c) resulted in some impairment in mitochondrial respiratory capacity in response to fatty acid substrate supply after six months. SignificanceSSB intake did not result in cardiac dysfunction or insulin resistance. However, early changes at the molecular level may increase risk in the longer term.

Protective efficacy of dinitrosyl iron complexes with reduced glutathione in cardioplegia and reperfusion.

Disturbed homeostasis of nitric oxide (NO) is one of the causes of myocardial ischemia/reperfusion (I/R) injury during open-heart surgery. This study was designed to explore mechanisms of action of dinitrosyl iron complexes with reduced glutathione ({(GS-)2Fe+(NO+)2}+, DNIC-GS) added to crystalloid cardioplegia or reperfusion solution in isolated working rat hearts. Hearts of male Wistar rats were subjected to cardioplegic arrest by St. Thomas' Hospital cardioplegic solution (STH) and normothermic global ischemia followed by reperfusion. DNIC-GS were used with STH or during early reperfusion. Lactate dehydrogenase (LDH) activity in the coronary effluent and myocardial contents of adenine nucleotides, phosphocreatine, and lactate were determined spectrophotometrically. Reactive oxygen species (ROS) formation in the coronary effluent and myocardial DNIC content was assessed by EPR technique. Cardioplegia or reperfusion with DNIC-GS significantly improved recovery of coronary flow and cardiac function compared with control. Carboxy-[2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidozoline-1-oxy-3-oxide] (C-PTIO), a selective NO scavenger, reduced/abolished protective action of DNIC-GS. Enhanced recovery of cardiac function with DNIC-GS reduced LDH release in the coronary effluent, augmented recovery of myocardial energy state, and decreased formation of ROS-generating systems at reperfusion. Beneficial effects of DNIC-GS were related to the transfer of [Fe(NO)2] cores to thiol groups of myocardial proteins to form intracellular DNIC pools. The study concluded that DNIC-GS is a promising adjunct agent for metabolic and antioxidant protection of the heart during cardioplegic arrest and reperfusion.

Mitochondrial integrity during early reperfusion in an isolated rat heart model of donation after circulatory death-consequences of ischemic duration.

Cardioprotection and graft evaluation after ischemia-reperfusion (IR) are essential in facilitating heart transplantation with donation after circulatory death. Given the key role of mitochondria in IR, we aimed to investigate the tolerance of cardiac mitochondria to warm, global ischemia and to determine the predictive value of early reperfusion mitochondria-related parameters for post-ischemic cardiac recovery. Isolated, working rat hearts underwent 0, 21, 24, 27, 30, or 33 minutes of warm, global ischemia, followed by 60 minutes of reperfusion. Functional recovery (developed pressure × heart rate) was determined at 60 minutes of reperfusion, whereas mitochondrial integrity was measured at 10 minutes of reperfusion. Functional recovery at 60 minutes of reperfusion decreased with ≥ 27 minutes of ischemia vs no ischemia (n = 7-8/group; p < 0.01). Cytochrome c, succinate release, and mitochondrial Ca2+ content increased with ≥ 27 minutes of ischemia vs no ischemia (p < 0.05). Ischemia at ≥ 21 minutes decreased mitochondrial coupling, adenosine 5'-triphosphate content, mitochondrial Ca2+ retention capacity, and increased oxidative damage vs no ischemia (p < 0.05). Reactive oxygen species (ROS) from reverse electron transfer increased with 21 and 27 minutes of ischemia vs no ischemia and 33 minutes of ischemia (p < 0.05), whereas ROS from forward electron transfer increased only with 33 minutes of ischemia vs no ischemia (p < 0.05). Mitochondrial coupling and adenosine 5'-triphosphate content correlated positively and cytochrome c, succinate, oxidative damage, and mitochondrial Ca2+ content correlated negatively with cardiac functional recovery (p < 0.05). Mitochondrial dysfunction occurs with shorter periods of ischemia than cardiac dysfunction. Mitochondrial coupling, ROS emission from reverse electron transfer, and calcium retention are particularly sensitive to early reperfusion injury, reflecting potential targets for cardioprotection. Indicators of mitochondrial integrity may be of aid in evaluating suitability of donation after circulatory death grafts for transplantation.

Abstract 17367: Infusion of the Ketone Body β-Hydroxybutyrate Improves Left Ventricular Systolic Function in an Animal Model of Heart Failure With Reduced Ejection Fraction

Introduction: In vitro, ketone bodies (KB) are the most energetically efficient fuel for myocardium. Ex vivo, KB infusion in the perfusion medium of working rat hearts increases the heat of combustion (produced energy) by 31%. However, there is no report about the in vivo effects of KB on LV function. We hypothesized that KB infusion in HFREF would improve energy production and thus LV systolic function. Methods: HFREF was induced in 15 pigs by 2-hour balloon occlusion of LAD: proximal LAD (n=8, severe HREF) and mid LAD (n=7, moderate HFREF). At 2 months, LV systolic function was evaluated during saline infusion and during infusion of the KB β-hydroxybutyrate. Severe HFREF animals underwent cardiac MRI for baseline LVEF, feature tracking strains, and contractile reserve (ΔLVEF under dobutamine 5μg/kg/min). Moderate HFREF pigs underwent invasive hemodynamic assessment (dP/dt) and 3D-echocadiography (3D-LVEF and 3D-strains). Simultaneous sampling from coronary artery and coronary sinus was performed to measure myocardial fuel consumption. Results: Proximal and mid LAD occlusion resulted in severe and moderate LV systolic dysfunction, respectively. In the severe HFREF, ketone infusion improved baseline LVEF, feature-tracking strains (both longitudinal and circumferencial strain), and contractile reserve. In the moderate HFREF, ketone infusion improved 3D-LVEF, 3D-strains and dP/dt (Table). Ketone infusion switched myocardial metabolism from glucose to ketone consumption. Conclusions: Continuous infusion of the KB hydroxybutyrate improves LV systolic function independent of LV systolic dysfunction severity via a shift in myocardial fuel metabolism away from glucose oxidation (energy inefficient) toward a more energy-efficient fuel like KB. This effect can explain the mechanism of action of the benefits of SGLT2 inhibitors in heart failure, as empagliflozin-induced mild kyperketonemia may increase LV systolic function and thus improve patient outcomes.